Heat exchanger, in particular for a power semiconductor

ABSTRACT

The heat exchanger comprises a casing divided into two chambers ( 10, 11 ) that are connected to each other by numerous parallel tubes ( 23 ) each extending from a bottom heat-exchange face ( 5 ) to a top face ( 6 ) on which a pressing force may be exerted. The cooling fluid passes over the faces ( 5  and  6 ) in full, enabling heat to be removed well with great uniformity. The head loss is moderate. The heat exchanger ( 1 ) is flexible enough to fit against the surfaces of the elements ( 3 ) to be cooled while being capable, by means of the tubes, of withstanding the required applied force. Possible application for cooling power semiconductors or any other component requiring cooling or heating.

The invention provides a heat exchanger and an arrangement making use of it, in particular an array of power transistors.

Certain power transistors dissipate such a large amount of heat energy that cooling is required. There are many existing heat exchangers, but their stiffness often makes it difficult to apply them with sufficiently good contact against such a heat-dissipator member that may present a surface that is uneven. It should also be recognized that many heat exchangers do riot have good capability for nor good uniformity in removing surface heat. Finally, certain heat exchangers experience considerable head losses in the cooling fluid.

Mention may be made of designs made up of an array of fins, generally designed to be cooled by air, without any particular fluid flowing therein, and that are unsatisfactory for the main application envisaged. Another type of heat exchanger includes internal plates arranged in spirals imposing turbulent flow on the heat exchanger fluid, the element for cooling being placed on a side face of the casing, beside the flow. Patent EP-A-0 613 179 describes such a design that possesses good cooling uniformity, but with large head losses and with stiffness that is too high, since all of the inside plates are pressing against the element to be cooled.

Another design is based on using internal corrugated plates defining cooling channels. In the particular embodiment of document EP-A-1 898 464, while flowing lengthwise along the corrugations, the heat exchange fluid is caused by slanting fins to approach the heat exchange surface and then to move away: its overall movement in the channels is sinuous. Those heat exchangers also present, in general, considerable stiffness, cooling temperature uniformity that is not very good, and heat-removal performance that is sometimes unsatisfactory.

The invention provides an improved heat exchanger, without the above-mentioned drawbacks and possessing, in particular, good flexibility allowing it to be applied on a member for cooling that is of irregular shape, and also possessing sufficient strength to withstand the desired application pressure, excellent heat-removal performance, and moderate fluid head loss.

In general, the invention provides a heat exchanger comprising: a casing made up of a bottom face, a top face, and a peripheral face; an array of parallel tubes extending inside the casing from the top face to the bottom face; an intermediate plate between the bottom face and the top face, extending to the peripheral face and dividing the inside of the casing into a bottom chamber and a top chamber; and entry and exit ducts for cooling fluid opening out respectively into the top chamber and the bottom chamber; the tubes extending through the intermediate plate and opening out into channels in the bottom chamber and the top chamber.

The invention also provides an arrangement comprising a heat-dissipator member, at least one such heat exchanger having its bottom face placed against the heat-dissipator member, and a press having a platten that presses the heat-dissipator member towards the heat exchanger.

The invention is described in more detail below with reference to the following figures, showing a purely illustrative embodiment of the invention, and in which.

FIG. 1 shows a complete arrangement, in central section;

FIG. 2 shows a heat exchanger in plan view;

FIG. 3 shows the inside of a heat exchanger;

FIG. 4 shows how the arrangement is pressed;

FIG. 5 shows one particular tube; and

FIGS. 6 and 7 show two embodiments of inserts for other particular tubes.

FIG. 1 shows an arrangement in accordance with the invention, having two heat exchangers 1 and 1′ disposed on either side of a planar array 2 of power transistors 3. The arrangement is more or less symmetrical, and the heat exchangers 1 and 1′ may be alike. The description therefore mainly concerns heat exchanger 1. It comprises a casing consisting of a peripheral face 4 that is thick and stiff, a bottom face 5 directed towards the transistors 3, and a top face 6 opposite from said bottom face 5 and that is plane, as is said bottom face. The bottom face 5 serves to exchange heat, and the top face 6 is used for applying pressure on the heat exchanger 1. Together these faces define a volume that is closed with the exception of an entry hole 7 and an exit hole 8 situated opposite from each other, as shown in FIG. 2. The bottom face 5 and the top face 6 are flexible, i.e. they are suitable for deforming in order to fit closely to the shapes in relief of the parts pressed against them.

The inside of the casing includes an intermediate plate 9 extending in all directions as far as the peripheral plate 4 and dividing the inside of the casing into a bottom chamber 10 and a top chamber 11 respectively adjacent to the bottom face 5 and to the top face 6. It also contains an array of tubes 23, which can be seen better in FIG. 3, extending from the bottom face 5 to the top face 6, being brazed thereto, and crimped in the intermediate plate 9 or otherwise fastened thereto. The tubes 23 extend in a tight array in at least the major fraction of the inside of the casing. The intermediate 9 plate is thinner than the peripheral face 4 and thicker than the bottom and top faces 5 and 6.

The flow of heat-removing fluid in the heat exchanger 1 is as follows. The fluid enters through the entry hole 7 in the top chamber 11, then infiltrates into the tubes 23 by means of channels 12 present between the tubes and the top face 6, in non-brazed portions of the junctions. The fluid flows along the tubes 23 through the intermediate plate 9, and emerges into the bottom chamber 10 by passing via channels 13 that are present between the tubes 23 and the bottom face 5. The fluid spreads out in the bottom chamber 10 before leaving it through the exit hole 8. All the fluid that is put into circulation therefore arrives on the bottom face 5 through which heat is exchanged and the fluid contributes to heat exchange, thereby providing good heat-removal performance. Head loss remains moderate because of the relatively short flow path length, because of the small number of obstacles and changes of direction, and because of the large quantity of tubes 23. Since the tubes 23 are arranged close together and convey substantially equal flow rates of fluid coming from a common top chamber 11, the removal of heat is more or less even across the entire surface area of the bottom face 5, and its temperature is therefore more or less even. Finally, the flexibility of the bottom and top faces 5 and 6 and even of the intermediate plate 9 makes it possible to exert continuous contact against the array 2 by applying pressure from the top face 6, with the tubes 23 nevertheless being stiff enough to prevent the heat exchanger 1 from being crushed, and to transmit the applied pressure thoroughly against an array 2.

The way pressure is applied to the arrangement is shown in FIG. 4. A platters 14 of a press pushes on the top face 6 of the heat exchanger 1, and an opposite platten 15 of the same press pushes the corresponding face of the heat exchanger 1′ towards the array 2.

The tubes 23 may be smooth; they may also be given a special shape, e.g. by providing them with helical grooves 20 on their inside faces (FIG. 5) or by inserting Archimedes' type screws therein (21 or 22) that are obtained by twisting flat or cross-shaped strips (FIGS. 6 and 7). All these elements improve the uniformity of flow in the tubes 23, while increasing the heat exchange surface area (especially the inserts), and therefore the heat-removal performance. 

1. A heat exchanger comprising: a casing made up of a bottom face (5), a top face (6), and a peripheral face (4); an array of parallel tubes (23) extending inside the casing from the top face (6) to the bottom face (5); an intermediate plate (9) between the bottom face and the top face, extending to the peripheral face and dividing the inside of the casing into a bottom chamber (10) and a top chamber (11); and entry and exit ducts (7, 8) for cooling fluid opening out respectively into the top chamber (11) and the bottom chamber (10); the tubes (23) extending through the intermediate plate and opening out into channels (12, 13) in the bottom chamber and the top chamber.
 2. A heat exchanger according to claim 1, characterized in that the tubes (23) are fastened inside the intermediate plate (9), to the bottom face (5) and to the top face (6), which faces are thinner than the peripheral face (4) and the intermediate plate (9).
 3. A heat exchanger according to claim 1 or claim 2, characterized in that the tubes (23) are provided with helical (20) fluting on their inside faces.
 4. A heat exchanger according to claim 1 or claim 2, characterized in that the tubes (23) contain helical inserts (21, 22). 